Active Caspase-1 Induces Plasma Membrane Pores That Precede Pyroptotic Lysis and Are Blocked by Lanthanides.

Canonical inflammasome activation induces a caspase-1/gasdermin D (Gsdmd)-dependent lytic cell death called pyroptosis that promotes antimicrobial host defense but may contribute to sepsis. The nature of the caspase-1-dependent change in plasma membrane (PM) permeability during pyroptotic progression remains incompletely defined. We assayed propidium(2+) (Pro(2+)) influx kinetics during NLRP3 or Pyrin inflammasome activation in murine bone marrow-derived macrophages (BMDMs) as an indicator of this PM permeabilization.

NLRP3 inflammasome signaling is activated by low-level lysosome disruption but inhibited by extensive lysosome disruption: roles for K+ efflux and Ca2+ influx.

Nucleotide-binding domain, leucine-rich-repeat-containing family, pyrin domain-containing 3 (NLRP3) is a cytosolic protein that nucleates assembly of inflammasome signaling platforms, which facilitate caspase-1-mediated IL-1β release and other inflammatory responses in myeloid leukocytes. NLRP3 inflammasomes are assembled in response to multiple pathogen- or environmental stress-induced changes in basic cell physiology, including the destabilization of lysosome integrity and activation of K(+)-permeable channels/transporters in the plasma membrane (PM). However, the quantitative relationships between lysosome membrane permeabilization (LMP), induction of increased PM K(+) permeability, and activation of NLRP3 signaling are incompletely characterized.

Caspase-8 as an Effector and Regulator of NLRP3 Inflammasome Signaling.

We recently described the induction of noncanonical IL-1β processing via caspase-8 recruited to ripoptosome signaling platforms in myeloid leukocytes. Here, we demonstrate that activated NLRP3·ASC inflammasomes recruit caspase-8 to drive IL-1β processing in murine bone marrow-derived dendritic cells (BMDC) independent of caspase-1 and -11. Sustained stimulation (>2 h) of LPS-primed caspase-1-deficient (Casp1/11(-/-)) BMDC with the canonical NLRP3 inflammasome agonist nigericin results in release of bioactive IL-1β in conjunction with robust caspase-8 activation.

K+ efflux agonists induce NLRP3 inflammasome activation independently of Ca2+ signaling.

Perturbation of intracellular ion homeostasis is a major cellular stress signal for activation of NLRP3 inflammasome signaling that results in caspase-1-mediated production of IL-1β and pyroptosis. However, the relative contributions of decreased cytosolic K(+) concentration versus increased cytosolic Ca(2+) concentration ([Ca(2+)]) remain disputed and incompletely defined. We investigated roles for elevated cytosolic [Ca(2+)] in NLRP3 activation and downstream inflammasome signaling responses in primary murine dendritic cells and macrophages in response to two canonical NLRP3 agonists (ATP and nigericin) that facilitate primary K(+) efflux by mechanistically distinct pathways or the lysosome-destabilizing agonist Leu-Leu-O-methyl ester.

Atherosclerosis and leukocyte-endothelial adhesive interactions are increased following acute myocardial infarction in apolipoprotein E deficient mice.

Objective: To determine the effect of myocardial infarction (MI) on progression of atherosclerosis in apolipoprotein E deficient (ApoE-/-) mice.

Methods And Results: MI was induced following left anterior descending coronary artery (LAD) ligation in wild-type (WT) (n=9) and ApoE-/- (n=25) mice. Compared to sham-operated animals, MI mice demonstrated increased intravascular leukocyte rolling and firm adhesion by intravital microscopy, reflecting enhanced systemic leukocyte-endothelial interactions.

P-selectin glycoprotein ligand-1 regulates adhesive properties of the endothelium and leukocyte trafficking into adipose tissue.

Rationale: Adhesive interactions between endothelial cells and leukocytes affect leukocyte trafficking in adipose tissue. The role of P-selectin glycoprotein ligand-1 (Psgl-1) in this process is unclear.

Objective: The goal of this study was to determine the effect of Psgl-1 deficiency on adhesive properties of the endothelium and on leukocyte recruitment into obese adipose depots.

Monocyte chemoattractant protein-1 deficiency protects against visceral fat-induced atherosclerosis.

Objective: To determine the role of monocyte chemoattractant protein-1 (Mcp-1) on the progression of visceral fat-induced atherosclerosis.

Methods And Results: Visceral fat inflammation was induced by transplantation of perigonadal fat. To determine whether recipient Mcp-1 status affected atherosclerosis induced by inflammatory fat, apolipoprotein E-deficient (ApoE(-/-)) and ApoE(-/-) and Mcp-1-deficient (Mcp-1(-/-)) mice underwent visceral fat transplantation.